Treatment of diseases and ailments of the body often benefit from short—or long-term infusion of drugs and/or other fluids. While such therapeutic substances may be administered extracorporally, e.g., via transcutaneous injection, many patient benefit from the consistent and repeatable dosage provided by an implantable infusion pump. Such pumps may be used in a variety of applications such as control of pain and/or spasticity. They are well-suited to deliver infusate fluids to a targeted delivery site such as an epidural or intrathecal space of the spinal canal, or a particular location within the brain.
Implantable infusion pumps are typically implanted subcutaneously, e.g., in the chest or abdominal cavity. The pump may incorporate a reservoir to hold the infusate fluid. A self-sealing, needle-penetrable septum may also be provided and is preferably located generally directly beneath the skin. The septum provides a fluid passageway that permits the reservoir to be refilled periodically via a transcutaneous injection. Accordingly, the pump reservoir can be filled or refilled without requiring surgical removal from the patient's body, and further without requiring any other significant surgical procedure.
The pump may also include a discharge outlet through which the therapeutic substance is directed during delivery. The outlet is typically connected to flexible medical tubing, e.g., a catheter, leading to the targeted delivery site. In addition to the reservoir, infusion pumps may further include a power source, a pump, and associated electronics to control delivery of the therapeutic substance to the patient in accordance with a prescribed schedule.
Active or programmable infusion devices using a pump or similar metering mechanism to deliver the desired drug dosage are commonly used. Active devices typically include a drug reservoir, a pump to transport the drug from the reservoir, and an outlet port coupled to a flexible catheter, the latter operable to carry the drug to the desired location within the body. Such devices may further include a battery to power the pump, as well as associated electronics to control various device parameters, e.g., pump flow rate. Some active devices may further include an antenna that permits remote programming of the device once implanted. An example of an active drug infusion device is the SYNCHROMED line of programmable pumps produced by Medtronic, Inc.
Regardless of what type of infusion device is utilized, a primary goal is to ensure that only a specific volume of the therapeutic substance is delivered to the patient. Yet, various factors may adversely impact precise substance delivery. For example, some medical devices may utilize a flexible reservoir that is exposed to surrounding tissue and thus to ambient pressure, e.g., the reservoir is not protected by a shell of the medical device. With such devices, the application of an external force may compress the reservoir and thus elevate reservoir pressure. The pump, seals, and other components downstream of the reservoir may then be exposed to this elevated pressure, potentially resulting in excess substance infusion and/or component (e.g., pump) damage.
Implantable infusion devices for delivering therapeutic substances to a patient using solenoid piston pumps are described in U.S. Patent Application Publication No. US 2002/0173773 (Olsen). Although these implantable infusion devices offer many advantages in areas such as, e.g., energy efficiency, size, compatibility with therapeutic substances, etc., further improvements in the implantable infusion devices are possible.
For example, further enhancements in, e.g., energy efficiency and/or accuracy may be possible by addressing the arrangement and use of valves to control the output of the pump.